Abstracts

Rationale: We have previously reported lateralized mesial temporal (MT) activation in response to a MSI auditory language paradigm. More activation in the right hemisphere of patients with left MTS and a relationship to Wada memory performance have led to speculation that MT activation may represent unilateral memory processing. The present investigation explores the relationship of MT activation to language classification in a further attempt to understand the interactions of language dominance, verbal memory and functional reorganization in patients with temporal lobe pathology.Methods: The subjects were 51 adult epilepsy or brain tumor surgery candidates who underwent MSI language mapping, the Wada test and neuropsychological evaluation. The MEG unit consisted of a 148-channel magnes 2500 WH system and data were analyzed using the single equivalent dipole (ECD) model across each whole hemisphere. The activation test was an auditory word recognition task in which subjects identified target words repeated on successive trials. The hemisphere with the most MT activity sites was identified for each patient. Wada memory was assessed with a maximum of 16 items presented prior to first motor return and calculated as a percent correct for each injection. The neuropsychological test battery included measures of IQ, verbal memory, verbal fluency as well as visual and auditory naming.Results: The patients were divided into left (n=22), right (n=13) and no MT activation (-MT, n=16) groups. 95% of the left MT patients were left language dominant on the Wada test, and 75% were left dominant on MSI. Of the right MT patients, 77% were left dominant on the Wada test and 46% were classified left dominant on MSI. The remaining right MT patients (n=7) were classified with atypical language lateralization on MSI and in every case, classification was at least partially discordant with the Wada test. The -MT group showed 63% and 78% left dominance on the Wada and MSI respectively. The three groups differed in left hemisphere Wada memory scores with the left group scoring highest at 73% correct, followed by 61% for the -MT group and a mean failing score of 49% for the right group (p<.05). In follow-up comparisons of the individual groups, only the left-right groups differed significantly (p=.01) There were no differences between the groups in IQ, baseline memory performance or verbal fluency. Performance on auditory naming was slightly higher in the left MT group (p<.05) compared to right or MT patients. . Conclusions: Patients with right MT activation are more likely to be classified with atypical language lateralization on MSI, often in disagreement with results of the Wada test. As a group, they also demonstrate impaired Wada memory performance in the left hemisphere. The possibility that these patients are relying more on right hemisphere processing in response to left hemisphere pathology remains to be determined. The question of why this might result in possibly erroneous language classification deserves further investigation.